Exceptional piezoelectricity, high thermal conductivity and stiffness and promising photocatalysis in two-dimensional MoSi2N4 family confirmed by first-principles

Chemical vapor deposition has been most recently employed to fabricate centimeter-scale high-quality single-layer MoSi 2 N 4 ( Science; 2020;369; 670 ). Motivated by this exciting experimental advance, herein we conduct extensive first-principles based simulations to explore the stability, mechanical properties, lattice thermal conductivity , piezoelectric and flexoelectric response, and photocatalytic and electronic features of MA 2 Z 4 (M = Cr, Mo, W; A = Si, Ge; Z = N, P) monolayers. The considered nanosheets are found to exhibit dynamical stability and remarkably high mechanical properties. Moreover, they show diverse electronic properties from antiferromagnetic metal to half metal and to semiconductors with band gaps ranging from 0.31 to 2.57 eV. Among the studied nanosheets , the MoSi 2 N 4 and WSi 2 N 4 monolayers yield appropriate band edge positions, high electron and hole mobilities, and strong visible light absorption , highly promising for applications in optoelectronics and photocatalytic water splitting. The MoSi 2 N 4 and WSi 2 N 4 monolayers are also predicted to show outstandingly high lattice thermal conductivity of 440 and 500 W/mK, respectively. For the first time we show that machine learning interatomic potentials trained over small supercells can be employed to examine the flexoelectric and piezoelectric properties of complex structures. As the most exciting finding, WSi 2 N 4 , CrSi 2 N 4 and MoSi 2 N 4 are found to exhibit the highest piezoelectric coefficients, outperforming all other-known 2D materials . Our results highlight that MA 2 Z 4 nanosheets not only undoubtedly outperform the transition metal dichalcogenides family but also can compete with graphene for applications in nanoelectronics, optoelectronic, energy storage/conversion and thermal management systems. • The intrinsic properties of MA 2 Z 4 (M = Cr, Mo, W; A = Si, Ge; Z = N, P) monolayers are explored. • An accurate methodology for the examination of flexoelectric properties is proposed using machine learning interatomic potentials. • WSi 2 N 4 , CrSi 2 N 4 and MoSi 2 N 4 monolayers exhibit the highest piezoelectric coefficients among all 2D materials . • MoSi 2 N 4 and WSi 2 N 4 monolayers show outstandingly high lattice thermal conductivity and mechanical strength. • MoSi 2 N 4 and WSi 2 N 4 nanosheets are promising for the applications in optoelectronics and photocatalytic water splitting.